Pak. J. Bot., 39(5): 1593-1608, 2007. APPRAISAL OF PHYSIOLOGICAL AND BIOCHEMICAL SELECTION CRITERIA FOR EVALUATION OF SALT TOLERANCE IN CANOLA (BRASSICA NAPUS L.) MOBINA ULFAT 1,3 , HABIB-UR-REHMAN ATHAR 2,3 , MUHAMMAD ASHRAF 3* , NUDRAT AISHA AKRAM 3 AND AMER JAMIL 4 1 Department of Botany, GC University, Lahore, Pakistan 2 Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan, Pakistan 3 Department of Botany, University of Agriculture, Faisalabad, Pakistan 4 Department of Biochemistry, University of Agriculture, Faisalabad, Pakistan Abstract Of Brassica species, canola (Brassica napus L.) is potentially important due to its good quality edible oil and potential to grow on salt affected areas. A greenhouse experiment was conducted to screen 34 local and exotic accessions of canola (Brassica napus L.) for salt tolerance and to identify suitable traits as selection criteria. Six week-old hydroponically grown plants of canola cultivars were subjected to 0 or 150 mM NaCl for five weeks. Various physiological and biochemical traits such as net CO 2 assimilation rate, stomatal conductance, transpiration rate, water use efficiency, leaf proline, leaf glycinebetaine, leaf Na + , leaf K + and leaf K + /Na + ratio, leaf osmotic potential and leaf relative water content were measured. All canola cultivars were ranked on the basis of relative salt tolerance using various physiological and biochemical attributes and then correlated with plant salt tolerance (plant growth) to identify the suitable selection criteria. Thus, the 34 lines were possible to categorize into three groups, i.e., salt sensitive, moderately salt tolerant, and salt tolerant. Dunkeld followed by Con-II, Rainbow were highly salt tolerant, while Westar, Balero, Oscar, RGS 003, Option-500 and Cyclone were salt sensitive. However, cvs BLN- 877, Haanza, Goliath, and Olga were also considered potential candidates as salt tolerant cultivars. According to the analysis of linear regression of the scores of the physiological traits against those of plant growth, except leaf K + , leaf osmotic potential and RWC, all physiological and biochemical traits were positively related with their salt tolerance. However, A and g s were found as the most suitable determinants. Overall, photosynthetic capacity, proline and GB accumulation ability, and ion discrimination can be used as potential biochemical or physiological selection criteria for salt tolerance in canola. Although leaf Na + , leaf K + /Na + ratio, proline and GB accumulation were positively related with salt tolerance, the strength of relationship was week. Introduction A great deal of research has provided a lot of information on salinity tolerance of plants with the main focus on water relations, photosynthesis and accumulation of various inorganic ions and organic metabolites (Munns, 2002; 2005; Ashraf, 2004). However, these determinants of salt tolerance vary amongst species and even among cultivars due to complex nature of the mechanism of salt tolerance (Ashraf, 1994; Flowers, 2004; Munns, 2007). In some comprehensive reviews Ashraf (2004) and Ashraf & Harris (2004) reported that metabolic sites at which salt stress damages plants are still not well understood and there are no well-defined plant physiological or biochemical selection criteria that could be used for improvement of salt tolerance in crops. However, there are a number of studies which show that intra-specific genetic variability for salt tolerance can be assessed by screening large number of lines/cultivars in saline conditions, * Corresponding author: ashrafbot@yahoo.com